This invention relates in general to apparatus for cutting limp sheet material and deals more particularly with improvements in cutting machines of automatic type which include a vacuum holddown system for compresing a layup of sheet material and holding it in a firmly fixed position on a support surface while a cutting instrument moves in cutting engagement with the layup in response to control signals received from a programmable controller. The vacuum holddown system may, for example, comprise a conveyorized vacuum holddown apparatus for compressing and holding successive contiguous segments of long layups to be cut which are substantially longer than the support surface. Thus, a layup or "marker" of pattern pieces used in the manufacture of garments, for example, may have overall dimensions of 6 feet (2 meters) in width and 24 feet (8 meters) or more in length. In cutting pattern pieces from such a marker, which has a length substantially greater than the length of the conveyorized cutting table, a first segment is positioned on the support surface defined by the table for cutting in a first operation. Upon completion of the first cutting operation, a second segment or bite is moved by the conveyor onto the table for cutting while the pattern pieces and scrap produced in cutting the first segment are removed.
Substantial energy is required to evacute the layup of sheet material, particularly after the material has been partially cut. Heretofore, various arrangements have been provided, in apparatus of the aforedescribed type, for paying out one or more non-destructable air-impermeable overlay sheets as the cutter moves in cutting relation to a layup, whereby to cover holes or kerfs formed in the layup by the cutting operation. One such apparatus designed to minimize leakage and loss of vacuum through cut sheet material is shown in U.S. Pat. No. 3,742,802 to Maerz, assigned to the assignee of the present invention. The apparatus disclosed by Maerz employs upon two air-impermeable overlays wound in opposite directions upon two spaced apart parallel rollers mounted on a cutting tool carriage supported for movement on and relative to a vacuum holddown table. The free ends of the overlays are secured at opposite ends of the holddown table, so that the overlay material is wound onto one of the rollers and payed-off the other of the rollers as the cutting carriage moves in a cutting mode in one and an opposite direction longitudinally of the holddown table. In this prior art, the only portion of the layup exposed during cutting is that portion below and in registry with the gap between the spaced apart rollers. The rolled overlays shown in U.S. Pat. No. 3,742,802 are not cut by the cutting tool, which is supported in the gap between the rollers, and may be repeatedly used.
A further approach to the problem is shown in U.S. Pat. No. 4,434,691 to LeBlond, also assigned to the assignee of the present invention. LeBlond provides a single non-destructable air-impermeable overlay for an automatically controlled cutting machine which includes a vacuum holddown conveyor table having an endless conveyor belt for moving successive segments of limp sheet material onto the conveyor table for cutting. The overlay comprises an elongated strip having its opposite ends wound onto rollers. One of the rollers is self-retracting and connected with the cutting carriage to pay-off or spread the overlay onto a layup of cut sheet material as the carriage moves longitudinally in one direction and retract the overlay as the cutting carriage moves in the opposite direction relative to the conveyor table during a cutting cycle. The other roller is motor driven and mounted proximate one end of the conveyor belt. An interconnecting portion of the overlay between the rollers is adapted to overlay the support surface of the conveyor table and any layup positioned thereon. As the cut layup is moved off of the cutting table, the overlay material is retrieved by the motor driven roller. At periodic intervals, portions of the overlay strip accummulated on the motor driven roller must be shifted back to the self-retracting roller mounted on the cutting carriage.
Still another arrangement for positioning a single non-destructable air-impermeable overlay in an apparatus of the aforedescribed general type is illustrated and described in my U.S. Pat. No. 4,452,113, entitled METHOD AND APPARATUS FOR SEALING CUT SHEET MATERIAL, issued June 5, 1984, and the assignee of the present invention. The apparatus disclosed in the latter patent includes a conveyorized vacuum holddown table and a sealing carriage which carries an air impermable overlay sheet wound on a self-retracting roller. The free end of the overlay sheet is mounted in fixed position proximate one end of the holddown table. The sealing carriage is supported for movement longitudially of the holddown table in coupled relation with the cutting carriage. Before the conveyor belt moves a cut segment of sheet material off of the holddown table the sealing carriage is uncoupled from the cutting carriage and the overlay is wound onto a self-retracting roller on the sealing carriage. The sealing carriage is simultaneously drawn by the overlay toward the one end of the holddown table where the sealing carriage remains parked while the cut segment is moved off the table.
While the arrangements illustrated and described in the aforementioned patents are satisfactory for most purposes, each of the aforedescribed mechanisms has some shortcomings. In some instances it may be desireable to inspect the initially cut pattern piece or pieces, as for example, during machine setup, or to remove a bundle of cut pattern pieces from the table before proceeding with the full cutting program. In the various apparatus hereinbefore described, it may be necessary to either return the tool carriage to its position of origin before the start of the cut, to enable windup of the overlay sheet, or to uncouple a sealing carriage from the tool carriage and allow it to move to a parked position in response to the self-retracting action of the roller carried by the sealing carriage, whereby to expose an initally cut pattern piece or pattern pieces. In the latter instance it is then necessary to return the cutting carriage to its positon of origin before the start of the cutting cycle, so that the sealing carriage may be coupled to it. In either instance, the cutting carriage must be moved to allow access to a partially cut layup to facilitate inspection of the initial cut, for example, before executing a complete cutting program. Such unproductive movement of the cutting carriage is time consuming and subjects the cutting apparatus to unnecessary wear.
Accordingly, it is the general aim of the present invention to provide an improved automatically controlled cutting machine wherein an air-impermeable overlay which seals material when cut is moved into overlaying relationship with an associated layup of material spread on a cutting table in response to movement of a cutting carriage during a cutting cycle and which includes means for moving the overlay either into or out of overlaying relation with a layup on the cutting table without moving the cutting carriage relative to the table.